1. Field of the Invention
The present invention relates generally to polymer compositions and, more particularly, to biodegradable polymer compositions, methods for making same and articles therefrom.
2. Description of the Related Art
Starches and modified starches have been the focus of considerable research interest in attempts to use these as fillers in order to decrease polymer costs and to use polymers that are biodegradable. Several recent examples, U.S. Pat. No. 5,384,187, issued Jan. 24, 1995, to inventors Uemura et al., U.S. Pat. No. 5,391,423, issued Feb. 21, 1995, to inventors Wnuk et al., and U.S. Pat. No. 5,412,005, issued May 2, 1995, to inventors Bastioli et al., all represent domestic and foreign based attempts to achieve biodegradable polymer compositions in which natural polymers such as starches have been added to hydroxy-functional polymers.
Recent biodegradable polymer compositions have included a starch or a modified starch and a hydroxy-functional polymer. An example of such a biodegradable polymer composition is disclosed in U.S. Pat. No. 5,852,078, issued Dec. 22, 1998, to inventors Willett et al. This biodegradable polymer composition includes the use of granular starch and thermoplastic poly(hydroxy ester ethers) (PHEE) made with various difunctional acids such as adipic acid. However, uses of this composition may be extremely limited due to the low glass transition temperature of the PHEE made with adipic acid. Most articles formed from this composition easily softened and lost their shape at high temperatures of up to and more than 100xc2x0 C.
Further, it is known to mix starch with a thermoplastic polyester such as poly(lactic acid) (PLA). It is also known that such a mixture is immiscible and any resultant article formed is brittle with poor material properties. Therefore, there is a need in the art to provide polymer compositions with hydroxy-functional polymers and thermoplastic polyesters that are useful in the manufacture of biodegradable plastics, but which are easily prepared and processed into articles that keep their shape at high temperatures.
Accordingly, the present invention is a polymer composition. The polymer composition includes a first component being a hydroxy-functional polymer of poly(hydroxy ester ether) (PHEE), a second component being a natural polymer and a third component being a thermoplastic polyester. The first component, second component and third component are compounded to form the polymer composition.
Also, the present invention is an article. The article includes a first component being a hydroxy-functional polymer of poly(hydroxy ester ether) (PHEE), a second component being a natural polymer and a third component being a thermoplastic polyester. The first component, second component and third component are compounded to form a polymer composition which is processed into the article.
Further, the present invention is a method of making a polymer composition. The method includes the steps of providing a first component being a hydroxy-functional polymer of poly(hydroxy ester ether) (PHEE), providing a second component being a natural polymer and providing a third component being a thermoplastic polyester. The method includes the steps of compounding the components to form a polymer composition.
The polymer compositions of the present invention are biodegradable and useful in various processes such as molding, extruding and casting to form molded articles and extruded sheets. The hydroxy-functional polymer may be as described by U.S. Pat. No. 5,171,820, issued Dec. 15, 1992, to inventors Mang et al., U.S. Pat. No. 5,496,910, issued Mar. 5, 1996, to inventors Mang et al., and PCT application published as International Publication No. WO 97/23564, on Jul. 3, 1997, to inventors Mang et al. Natural polymers for mixture with the hydroxy-functional polymers include polysaccharides, modified polysaccharides, naturally-occurring fibers, and particulate fillers. Particularly preferred as the natural polymer are starches. The thermoplastic polyesters for mixture with the natural polymers and hydroxy-functional polymers include poly(lactic acid) (PLA), bionolle, cellulose acetate, polycaprolactone and polyhydroxy(butyrate-co-valerate) (PHBV).
One advantage of the present invention is that new polymer compositions are provided which are useful in the manufacture of biodegradable plastics. Another advantage of the present invention is that a method is provided of making such polymer compositions. Yet another advantage of the present invention is that articles are easily prepared from such polymer compositions that keep their shape at high temperatures of up to and more than 100xc2x0 C. Still another advantage of the present invention is that the polymer compositions contain starch and a hydroxy-functional polymer such as poly(hycroxy ester ether) (PHEE) and a thermoplastic polyester such as poly(lactic acid) (PLA). A further another advantage of the present invention is that the method compounds the composition in at least one compounding step. Yet a further advantage of the present invention is that the compounded composition is pelletized for further processing in various processes such as injection molding. Still a further advantage of the present invention is that the polymer compositions are biodegradable and allow molded items to be formed such as planter pots, disposable razors, cutlery, pen casings, etc., with little concern of softening at high temperatures of up to and more than 100xc2x0 C.
Other features and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the subsequent description, examples and the appended claims.
Broadly, the present invention is a polymer composition comprising three main components: the first component is a hydroxy-functional polymer, more particularly, a hydroxy-functional polyester having a repeating structure as will hereinafter be described. The hydroxy-functional polymer may be, for example, a thermoplastic poly(hydroxy ester ether) (PHEE). The second component is a natural polymer. The natural polymer may be, for example, a polysaccharide, a modified polysaccharide, or a naturally occurring fiber or particulate filler, but preferably is starch or a modified starch. The third component is a thermoplastic polyester. The thermoplastic polyester may be, for example, a thermoplastic poly(lactic acid) (PLA).
While the amount of the hydroxy-functional polymer selected for use depends on a variety of factors, including the specific polymer employed and the desired end uses of the composition, in general hydroxy-functional polymers can be present in an amount of from 1 to 99 wt. %, preferably from 1 to 95 wt. %, and most preferably from 10 to 90 wt. %, based on the total weight of the composition. Preferably, the thermoplastic polyester is a poly(lactic acid) (PLA), present in amounts of about equal to or greater than the amount of the hydroxy-functional polymer used in the formulation of the composition.
Natural polymers contemplated for use include biodegradable organic fillers, such as cellulose and other fibers and the like, which are well known. Naturally occurring fibers or particulate fillers which can be employed in the practice of the present invention for preparing the composition are, for example, wood flour, wood pulp, wood fibers, cotton, flax, hemp, or ramie fibers, rice or wheat straw, chitin, chitosan, cellulose materials derived from agricultural products, nut shell flour, corn cob flour, and mixtures thereof. Polysaccharides which can be employed in the practice of the present invention for preparing the composition are the different starches, celluloses, hemicelluloses, gums, pectins, and pullulans. Polysaccharides are known and are described, for example, in Encyclopedia of Polymer Science and Technology, 2nd edition, 1987.
Modified polysaccharides which can be employed in the practice of the present invention for preparing the composition are the esters and ethers of polysaccharides, such as, for example, cellulose ethers and cellulose esters, or starch esters and starch ethers. Modified polysaccharides are known and are described, for example, in Encyclopedia of Polymer Science and Technology, 2nd edition, 1987.
The natural polymer is in a granular form (hereinafter referred to as the xe2x80x9cgranular embodimentxe2x80x9d). When practicing the granule embodiment of the present invention, the granules of natural polymer preferably will have a particle size of less than about 100 xcexcm, and more preferably have a particle size of up to about 50 xcexcm and a water content of less than about 15 wt. %, more preferably less than about 10 or 11 wt. %. In the granule embodiment, the three main components may be admixed in varying amounts. The natural polymer may be present in a trace amount or in greater amounts up to about 70 wt. %.
Suitable Hydroxy-Functional Polymers
The preparation and structures for hydroxy-functional polymers, such as hydroxy-functional polyesters, suitable in practicing the present invention may be as described by U.S. Pat. No. 5,171,820, issued Dec. 15, 1992, to inventors Mang et al., and U.S. Pat. No. 5,496,910, issued Mar. 5, 1996, to inventors Mang et al., the disclosures of which are hereby incorporated in their entirieties by reference. Such useful hydroxy-functional polyesters for the present invention may be prepared from base-catalyzed nucleophilic addition of suitable acids to epoxies, which reaction generates both an ester linkage and a pendent hydroxyl group. Transesterification and cross linking reactions are eliminated through use of quaternary ammonium halide salts as initiators for the reaction of diacids with diglycidyl ethers, providing convenient preparation of high molecular weight, thermoplastic, hydroxy-functional polyesters in ether solvents at temperatures from 80xc2x0 C.-160xc2x0 C. Data provided by the Dow Chemical Company (manufacturer of hydroxy-functional polyesters such as described by U.S. Pat. Nos. 5,171,820 and 5,496,910) indicates the biodegradable nature of these polymers through the ability of various soil bacteria (such as Pseudomonas putida) to use the synthetic polymers as a substrate for cell culture growth.
Representative structures for suitable hydroxy-functional polyesters in practicing the present invention are represented by Formula A (where n provides a sufficient molecular weight, such as for example a m.w. of about 50,000-100,000. Higher molecular weights are preferred due to higher strength.

In Formula A each of R1 and R2 is individually a divalent organic moiety which is predominately hydrocarbon, each R3 is individually a hydrogen or lower alkyl, y is a fraction from 0 to 0.5 and x is a fraction from about 0.05 to about 0.4. Typically Y is hydrogen or glycidyl and Yxe2x80x2 is glycidyl arylene ether, glycidyl alkyene ester, glycidyl alkylene ether or glycidyl arylene ester.
Thus, suitable polyesters have repeating units represented by Formula B (where each of R1, R2, R3, x and y are as defined above)

Such polyesters may be prepared from diglycidyl esters of an aliphatic diacid such as adipic acid due to the ready availability and reasonable price for adipic acid as a source of reactant. Other particularly preferred polyesters may be prepared from dihydric phenols, such as hydroquinone.
Four particularly preferred hydroxy-functional polyesters, used extensively to illustrate (but not to limit) the present invention, are sometimes hereinafter designated xe2x80x9cBIS CHD,xe2x80x9d xe2x80x9cBIS adipic,xe2x80x9d xe2x80x9cHQ DDCAxe2x80x9d and xe2x80x9cBIS DDCA.xe2x80x9d These polymers will include some repeating unit structures, where the repeating units are illustrated respectively by Formulas C-F.




In Formulas C-F, xe2x80x9cnxe2x80x9d preferably is as earlier described.
Other suitable hydroxy-functional polymers for practicing the present invention are described by Formula I in PCT application published as International Publication No. WO 97/23564, on Jul. 3, 1997, to inventors Mang et al. The below illustrated repeating structure described by U.S. Pat. No. 5,496,910, issued Mar. 5, 1996, to inventors Mang et al., incorporated herein by reference and designated here as Formula I is believed to encompass Formula B.
Thus, the Formula I polymers have repeating units represented by the formula: 
wherein Ra individually represents a divalent organic moiety which is predominately hydrocarbylene (where the term xe2x80x9chydrocarbylenexe2x80x9d means a divalent aliphatic hydrocarbon moiety, such as alkylene, alkenylene or cycloalkylene having 2 to 20 carbons and optionally containing a heteroatomic group, such as oxygen, sulfur, amino, sulfonyl, carboxyl, carbonyl or sulfoxyl, in the chain or pendant thereto) or a combination of different organic moieties which are predominantly hydrocarbylene; Rc is 
wherein Rb is a divalent organic moiety which is predominantly hydrocarbylene or 
Re is hydrogen or lower alkyl, such as methyl, ethyl, butyl and propyl, more preferably hydrogen, Rf is independently an organic moiety which is predominantly hydrocarbylene, Rg is independently hydrogen or methyl, nxe2x80x2 is an integer from about 0 to about 100, and xxe2x80x2 and yxe2x80x2 are independently integers from 0 to 100.
Representative divalent organic moieties useful as Ra, Rb, and Rf include alkylene, cycloalkylene, alkylenearylene, poly(alkyleneoxyalkylene), alkylenethioalkylene, alkylenesulfonylalkylene, alkylene substituted with at least one hydroxyl group, cycloalkylene substituted with at least one hydroxyl group, alkylenearylene substituted with at least one hydroxyl group, poly(alkyleneoxyalkylene) substituted with at least one hydroxyl group, alkylenethioalkylene substituted with at least one hydroxyl group, alkylenesulfonylalkylene substituted with at least one hydroxyl group, arylene, dialkylenearylene, diaryleneketone, diarylenesulfone, diarylene oxide, and diarylene sulfide.
In the more preferred hydroxy-functional polyethers, Ra, Rb and Rt are independently methylene, ethylene, propylene, butylene, pentamethylene, hexamethylene, heptamethylene, octamethylene, nonamethylene, decamethylene, dodecamethylene, 1,4-cyclohexylene, 1,3-cyclohexylene, or 1,2-cyclohexylene optionally substituted with at least one hydroxyl group, p-phenylene, m-phenylene, or 2,6-naphthalene, diphenyleneisopropylidene, sulfonyldiphenylene, carbonyldiphenylene, oxydiphenylene, or 9,9-fluorenediphenylene and nxe2x80x2 is from 0 to 10.
The polymers represented by Formula I may be prepared by reacting diglycidyl esters or aliphatic or aromatic diacids such as diglycidyl terephthalate, or diglycidyl ethers of dihydric phenols or alcohols with aliphatic or aromatic diacids such as adipic acid or terephthalic acid. Thus, suitable polymers for the present invention can be prepared by reacting a hydroxy-functional aliphatic diacid, optionally in the presence of another diacid, with a diglycidyl ether or diglycidyl ester or a mixture of diglycidyl ethers or diglycidyl esters at conditions sufficient to cause the acid moieties to react with the epoxy moieties to form a polymer backbone having ester linkages, as described in U.S. Pat. No. 5,171,820.
Natural Polymers
Among the natural polymers suitable for practicing the present invention are the particularly preferred starches. Starch is a low-cost and abundant natural polymer composed of amylose and amylopectin. Amylose is essentially a linear polymer having a number average molecular weight in the range of 100,000-500,000, whereas amylopectin is a highly branched polymer having a number average molecular weight of up to several million. Unmodified, natural starches are obtained in granular form and may be derived from cereals or grains (such as corn, wheat, rice and sorghum), roots (such as, cassava), legumes (such as peas), and tubers such as potato and canna. Such starch granules typically have a particle size less than about 50 xcexcm, which is the preferred particle size when practicing the granule embodiment. While less preferred, flours whose contents are predominately starch, and which may also contain protein, oil and fiber, are operative in the present invention. While such other natural polymers are used for granular embodiment formulations, they will be processed so as to be in granular form and preferably will have a relatively uniform particle size of about 50 xcexcm or less.
Starch granules for use in the granule embodiment will normally have a water content of less than about 15 wt. %, more preferably less than about 10-11 wt. %. As will be exemplified, granules may be pre-dried to less than about 1% moisture before compounding. Although preferred, pre-drying is not necessary.
Derivatized (modified) starches are also suitable for use in the present invention. xe2x80x9cDerivatized starchesxe2x80x9d is meant to include starches which have been chemically treated so as to form starch esters, starch ethers, and cross-linked starches. xe2x80x9cModifiedxe2x80x9d is meant that the starch can be derivatized or modified by typical processes known in the art (e.g. esterification, etherification, oxidation, acid hydrolysis, cross-linking and enzyme conversion). Typically, modified starches include esters, such as the acetate ester of dicarboxylic acids/anhydrides. Particularly useful are the alkenyl-succinic acids, anhydrides, ethers (such as the hydroxyethyl and hydroxypropyl starches), starches oxidized with hypochlorite, starches reacted with cross-linking agents such as phosphorus oxychloride, epichlorhydrin, hydrophobic cationic epoxides, and phosphate derivatives prepared by reaction with sodium or potassium orthophosphate or tripolyphosphate and combinations thereof. These and other conventional modifications of starch are described in publications such as Starch: Chemistry and Technology, 2nd edition, editor Whistler et al., and Starch Derivatives: Production and Uses, Rutenberg et al., Academic Press, Inc. 1984.
For example, starch esters may be prepared using a wide variety of anhydrides, organic acids, acid chlorides, or other esterification reagents. Examples of anhydrides are acetic, propionic, butyric, and so forth. Further, the degree of esterification can vary as desired, such as from one to three per glucosidic unit of the starch, or as appropriate given the number of hydroxyl groups in the monomeric unit of the natural polymer, if selected to be other than starch. Similar or different esterified natural polymers, with varying degrees of esterification, can be blended together for practicing the present invention. Although esterified starches are stable to attack by amylases, in the environment the esterified starches are attached by microorganisms secreting esterases which hydrolyze the ester linkage.
Starch esters tend to be hydrophobic in contrast to starch raw materials (that is, derived by usual techniques from natural sources such as corn). Thus, depending upon the particular application, one may prefer to choose an hydrophobic starch ester rather than a hydrophilic starch in formulating compositions of the present invention.
Although starches are preferred for use as the natural polymers, particularly due to ready availability and low cost, but as earlier noted, other suitable natural polymers (in or prepared to be in granular form of a suitable particle size) are hydroxyl containing polymers such as cellulose, hemicellulose, chitin, guar gum, locust bean gum, pectin, xanthan, algin, agar, and dextran. Some of these can play the role of filler, also. Excellent results have been obtained with both granulated guar gum and cellulose powder.
Suitable Thermoplastic Polyesters
The composition includes a thermoplastic polyester. Among the thermoplastic polyesters, a poly(lactic acid) (PLA) is preferred. The PLA is prepared and used in a pelletized form. Examples of other suitable thermoplastic polyesters include polyhydroxy(butyrate-co-valerate) (PHBV), bionolle, cellulose acetate and polycaprolactone. It should be appreciated that these thermoplastic polyesters are conventional and known in the art.
The thermoplastic polyesters may be prepared with additives to increase the rate of crystallization. For example, an additive such as boron nitride may be added to a thermoplastic polyester such as poly(lactic acid) (PLA) to increase the rate of crystallization of the PLA. It should be appreciated that other suitable additives may be added to the thermoplastic polyester to increase the crystallization.
Other Components
A plasticizer can be added to the inventive compositions to achieve greater material processability and product flexibility, although plasticizers typically soften the compositions in which they are included. This is not always true, however, of compositions of the present invention, as will be discussed hereinafter. Molded articles prepared from blends including plasticizers preferably use plasticizers that are biodegradable. Examples of biodegradable plasticizers include various esters, such as phthalate esters, and various other biodegradable esters known in the chemical arts.
Inorganic fillers can be added, such as talc, calcium carbonate, diatomaceous earth, and so forth.
Other optional components known in the art, including, but not limited to, anti-blocking agents, anti-static agents, slip agents, pro-heat stabilizers, antioxidants, pro-oxidant, and additives may be incorporated, depending upon the application.
Method of Making
A method, according to the present invention, is provided for making a polymer composition. In general, the method includes providing a first component being a hydroxy-functional polymer, providing a second component being a natural polymer such as starch and providing a third component being a thermoplastic polyester such as poly(lactic acid) (PLA). The method includes mixing these components in a single screw extruder, a twin screw extruder, a Banbury mixer, a roll mill or any intensive mixer at a temperature and for a time sufficient to provide an intimate, well-dispersed mixture of the components. Preferably, the components are brought together and compounded in an appropriate melt extruder from which the blend is extruded in the form of strands or sheets. The strands or sheets are then pelletized and molded into articles by conventional processes such as injection molding.
The method may include the step of forming bars from the sheets. The method may include the step of heating the polymer composition or formed bars for a predetermined time period such as up to 60 minutes and at a predetermined temperature such as 120xc2x0 C. to increase high temperature stability. It should be appreciated that other additives or treatments may be used to impart high temperature stability of the formed bars. It should also be appreciated that such additives or heating causes an annealing of the polymer composition to increase high temperature stability thereof.